I guess life goes on, and it should; but your ex should have told you he was introducing your son to his new girlfriend. Your son may have alot of questions, you shouldn't be kept in the dark; it's your son with him, together. it would be common courtesy just to let you know he's rethought his decision and wants to be open with your son about his new life.
remind him of what you discussed and that he has no reason to get mad. If he wont listen write it down for him. And then get divorced asap. Get custody.
Yeah....I don't get it honestly.<br />
Just get a lawyer if it's gonna be like that up to you though of course.